Cardiotomy reservoirs which reclaim blood drawn from a surgical site by defoaming and filtering the blood to remove foreign matter are well known. References which describe various cardiotomy reservoir structures include U.S. Pat. Nos. 3,507,395; 3,768,653; 3,891,416; 3,993,461, 4,157,965; 4,164,468; 4,208,193; 4,243,531; 4,705,497; and 4,743,371.
Typically, before it is oxygenated and returned to the body, blood which has been cleansed and defoamed in a cardiotomy reservoir is combined with blood extracted from a vein in the patient's body. To simplify the necessary connections for such procedures and to reduce the volume of the extracorporeal blood circuit, it has been proposed that cardiotomy blood and venous blood be combined in a cardiotomy reservoir and the combined fractions directly fed into an oxygenator. The depth filter media used in modern cardiotomy reservoirs, however, can damage healthy cells, especially under high pressures and, therefore, blood obtained directly from a venous shunt which is uncontaminated by foreign matter should not be forced through such filter media if possible.
Combined cardiotomy and venous return reservoirs which provides separate flow paths into common collection reservoirs for venous return blood obtained and for cardiotomy blood are described in U.S. Pat. Nos. 4,705,497 and 4,737,139.
U.S. Pat. No. 4,705,497 describes a combined cardiotomy and venous return reservoir in which the venous blood does not pass through any filtering or defoaming element and in which the venous and cardiotomy blood separately enter a pooling reservoir at different levels. The device includes no means to assure positive mixing of the blood fractions. The device of U.S. Pat. No. 4,737,139 has a significant disadvantage in that the blood from the two sources is never positively mixed. In this device the cardiotomy blood is filtered through reticulated polyurethane foam defoaming element, a felt depth filter and a mesh fabric screen while the venous blood is only passed through the polyurethane foam and mesh fabric elements. The device is arranged in such a manner that the venous and cardiotomy blood fractions have separate flow paths into the common reservoir with the venous blood entering the common collection reservoir below the cardiotomy blood. This flow pattern can result in significant layering of the blood, especially since the exit port is at the bottom of the collection reservoir and the venous blood typically is fed into the device at a much higher rate than cardiotomy blood.